基于Ce变质处理的TWIP钢凝固组织细化

Solidification Structure Refinement in TWIP Steel by Ce Inoculation

通过真空感应熔炼制备了成分为Fe-22Mn-0.65C的奥氏体TWIP钢,揭示了Ce含量及过热度对TWIP钢凝固组织细化的影响。基于FactSage 7.0热力学软件及错配度模型预测了Ce在TWIP钢中的变质产物及其非均质形核有效性,采用OM、SEM、EBSD、EPMA等手段对不同条件下凝固组织变质处理效果进行定量研究。结果表明,随Ce含量升高,其在TWIP钢中的反应产物由Ce2O3向Ce2O3+少量Ce2O2S转变,而2种粒子理论上均可作为有效形核核心;Ce变质处理后,TWIP钢试样铸态组织等轴晶率从25%升至72%,等轴晶平均尺寸由480μm减小到130μm,Mn元素偏析比由1.61降至1.41;降低变质处理温度时,含Ce粒子团聚倾向减小,TWIP钢凝固组织细化的效果更显著。本工作中建议的变质处理参数为过热度20℃时加入(0.02%~0.04%)Ce。

Twinning-induced plasticity(TWIP)steel represents a novel grade of advanced high strength and ductility with significant potential for automotive industry.However,high alloying in TWIP steel leads to the inhomogeneous solute distribution and anisotropic local deformation.It is well known that the refinement of solidification structure is an effective solution to the above defects.Much attention has been paid to heterogeneous nucleation by Ce particles,acting as nucleating sites in liquid steel.The present work focuses on how Ce content and casting parameters affect the refinement of solidification structure in Fe-22Mn-0.65C TWIP steel,aiming to provide an effective technology in high alloy steel production.The reaction products of Ce inoculation were predicted by thermodynamics software FactSage 7.0 and their effectiveness of heterogeneous nucleation was estimated by lattice misfit model.The solidification structure refinement by Ce inoculation under different conditions was experimentally studied by OM,SEM,EBSD and EPMA.The results show that,with increasing Ce content the reaction products transferred from Ce2O3 to Ce2O3+a small amount of Ce2O2S,and both kinds of particles can act as heterogeneous nucleation cores theoretically.For as-cast solidification structure,the ratio of equiaxed grain area increased from 25%to 72%,average equiaxed grain size decreased from 480μm to 130μm and the segregation ratio of Mn decreased from 1.61 to 1.41.Meanwhile,the tendency of particle agglomeration was weakened by lowering inoculation temperature,resulting in the improvement structure refinement.In this work,the recommended inoculation parameters are concluded as(0.02%~0.04%)Ce with superheat of 20℃.